Objective:To verify the existence of extraradicular biofilm of teeth with radiographically visible chronic periapical lesion and to observe the distribution and viability of extraradicular bacteria using confocal laser scanning microscopy(CLSM). Methods:Ten single-rooted teeth with periapical radiolucent areas were collected. Five single-rooted teeth extracted for orthodontic reasons were selected as controls. All of the roots were embedded in methylmethacrylate after staining with LIVE/DEAD■ BacLightTM Bacterial Viability Kits. Then,five evenly distributed transverse sections(1 mm thick)were cut from the apex to the corona. Finally,the sections were examined by CLSM. Results:There were weak auto-fluorescence signals in the control group. After adjusting the viewing conditions to obtain a baseline,at which no fluorescence was detectable in the control group specimens,8 of the 10 disease group teeth showed positive fluorescence signals on the external root surfaces. The distribution of extraradicular bacteria was extensive within a 2~3 mm range from the root tip to the corona. On 68% of optical views,the intensity of green fluorescence signals was stronger than that of red fluorescence signals. Conclusion:There were live and dead extraradicular bacteria on the external root surfaces of teeth with chronic periapical periodontitis.